Synthesis reactivity and mechanistic studies on 0X0, alkoxo and tertiary phosphine derivatives of niobium and tantalum

Abstract

The research described in this thesis is directed towards the development of the organometallic and coordination chemistry of niobium and tantalum with tertiary phosphine and oxygen containing ligands. Chapter 1 highlights the influence of tertiary phosphine ligands of various areas of organometallic and coordination chemistry. Chapter 2 describes syntheses and reactivity studies on several half-sandwich, tertiary phosphine complexes including (η(^5)-C(_5)H(_5))TaC1(_2)- (PMe(_3))(_3), (η(^5)-C(_5)Me(_5))TaC1(_2)(PMe(_3))(C0)(_2) and the paramagnetic, d(^2)-complex, (η(^5)-C(_5)Me(_5))TaCl(_2)(PMe(_3))(_2).Chapter 3 describes the synthesis and characterisation of ring and phosphine metallated isomers of (η(^5)-C(_5)Me(_5))Ta(PMe(_3))(_2), viz. (η(^7)-C(_5)Me(_3)-(CH(_2))(_2))Ta(H)(_2)(PMe(_3))(_2) and (η(^5)-C(_5)Me(_5)Me(_5))Ta(PMe(_3))(H)(_2)( η(^2)-CHPMe(_2)) respectively, Subsequently, Chapter 4 describes aspects of the reactivity and derivative chemistry of (η(^5)-C(_5)Me(_5))Ta(PMe(_3))(H)(_2)(η(^2)-CHPMe(_2)). The exploitation of reversible hydrogen migrations has facilitated the preparation of a number of complexes including, (η(^5)-C(_5)Me(_5))Ta(dmpe)- (H)(η(^2)-CH(_2)PMe(_2)) and (η(^5)-C(_5)Me(_5))Ta(C0)(_2)(PMe(_3))(_2), whilst reactions with alkyl halides or olefins result in the retention of the Ta(η(^2)-CHPMe(-2)) moiety, eg. (η(^5)-C(_5)Me(_5))Ta(PWe(_3))HX(η(^2)-CHPMe(_2)); (η(^5)_C(_5)Me(_5))TaX(_2)(η(_2)-CHPMe2) (X = CI, Br, I) and (η(^5)-G(_5)We(_5))Ta(CH(_2)CH(_2)CWe(_3))(_2)(η(^5)-CHPMe(_2)). Chapters 5 and 6 develop the use of Me(_3)SiOR (R = Me, Et, SiMe(_3)) reagents as sources of the oxygen ligands '0' and 'OR' for the mild, controllable synthesis of transition metal oxyhalides and alkoxyhalides. Chapter 5 describes various niobium compounds including Nb(0)Cl(_3) and Nb(0)C1(_3)L(_2) (L = CH(_3)CN, THF) and a number of aryloxide and tertiary phosphine derivatives of Nb(0)C1(_3). Chapter 6 describes several half - sandwich tantalum systems including (η(^5)-C(_5)Me(_5))TaC1(_3). OR (R = Me, Et, C(_3)H(_5), Re0(_3)), [(η(^5)-C(_5)Me(_5))TaC1(_3)](_2)(µ-0) and (η(^5)-C(^_5)Me(_5))Ta(0)C1(_2) Chapter 7 gives experimental details for Chapters 2-6.